PIFA-promoted intramolecular oxidative cyclization of pyrrolo- and indolo[1,2-]quinoxalino-appended porphyrins: an efficient synthesis of ,β-pyrrolo- and indolo[1,2-]quinoxalino-fused porphyrins.

We have developed an efficient protocol for the synthesis of ,β-pyrrolo- and indolo[1,2-]quinoxalino-fused porphyrin systems 7-9 by PIFA-promoted intramolecular oxidative cyclization of easily accessible -pyrrolo- and indolo[1,2-]quinoxalino-appended porphyrins 6a-j. The absorption spectra of ,β-pyrrolo- and indolo[1,2-]quinoxalino-fused porphyrins 7-9 displayed bathochromic shifted (100-150 nm) and broadened Soret bands and Q bands in addition to intense band near IR region. The indolo[1,2-]quinoxalino-fused porphyrin 9bZn with lower fluorescence quantum yield (0.003) and reduced energy gap (∼1.3 eV) was found to sensitize singlet oxygen effectively.